High-molecular, thermoplastic, aromatic polycarbonates are used in numerous technical fields of use, because of their typical tough and elastic properties. A disadvantage is their difficulty of mould release when injection moulded, which frequently results in relatively long cycle times. However, for economic and technical reasons it is desirable to shorten the cycle times as far as possible in order to produce a larger number of mouldings per unit time on the injection moulding machines. This can be achieved by mould release at higher temperatures. It is therefore desirable to modify the polycarbonate melt in such a way that the release of the moulding from the mould wall takes place with low release forces and at high temperatures, without sticking of the solidified melt. Ease of mould release at high temperatures is also particularly desirable for complicated mouldings which are processed in moulds comprising parts which cannot be cooled (for example webs, cores and the like). Undesirable sticking of the mouldings and damage to the moulds on detaching the mouldings (breakage of pins and the like) are a frequent consequence, coupled with extended time losses.
Hitherto, long-chain aliphatic carboxylic acid esters of monohydric and trihydric alcohols, according to DOS (German Published Specification) 2,064,095 (Le A 13 461) and DOS (German Published Specification) 2,220,185 (Le A 14 329) have been added in order to improve the ease of mould release of the aromatic polycarbonates. However, a disadvantage is the deterioration in mechanical properties on prolonged heat exposure, as a result of which the aromatic polycarbonates which have been rendered easily releasable from the mould in accordance with DOS (German Published Specification) 2,064,095 and DOS (German Published Specification) 2,220,185 no longer meet certain technical requirements. A further disadvantage is the high volatility of the fatty acid esters of glycerol, which manifests itself as a particular disadvantage at the high temperatures at which polycarbonate is processed.
Accordingly, it was an object of the present invention to prepare high-molecular, thermoplastic, aromatic polycarbonates which on the one hand show adequate mould release behaviour for a wide range of technical applications and on the other hand exhibit a level of mechanical properties which is comparable, even after exposure to heat, to that of the corresponding aromatic polycarbonates which do not contain mould release agent. The mould release behaviour at an elevated mould temperature, whereby the advantages described above are achieved, is particularly desirable.